1. Field of the Invention
The present invention relates to a driving circuit for a liquid crystal display (LCD) device. More particularly, the present invention relates to a driving circuit for an LCD device, a method of manufacturing the driving circuit and a display device having the driving circuit.
2. Description of the Related Art
A liquid crystal display (LCD) device has advantageous characteristics such as reduced thickness, light weight, low power consumption, and has good resolution, color reproducibility, and display quality. Thus, the LCD device, which is a type of flat panel display device, is being widely used and intensively researched.
The LCD device typically includes an LCD panel having a thin-film transistor (TFT) array substrate, a color filter substrate, a liquid crystal layer located between the TFT array substrate and the color filter substrate, a backlight assembly disposed under the LCD panel to serve as a light source, and a driving circuit part disposed at a peripheral portion of the LCD panel to drive the LCD panel. The LCD panel includes two glass substrates (the TFT array substrate and the color filter substrate mentioned above), a plurality of pixels disposed between the two glass substrates and arranged in a matrix shape on the thin-film transistor (TFT) array substrate and for each pixel a switching element such as a TFT for controlling signals provided to the pixel.
The driving circuit part includes a printed circuit board (PCB) on which parts for generating various signals such as a control signal, a clock signal, and a data signal, are mounted. A driving circuit that is an LCD driver integrated circuit (IC) (LDI) is connected to the LCD panel and the PCB to apply a signal to wirings formed on the LCD panel. The LCD driver integrated circuit includes a set of bonding pads with each bonding pad including a metal bump. The surface to which the driver integrated circuit is to be mounted is provided with a matching set of pads. The driver integrated circuit is mounted on the surface by bonding the set of bonding pads to the matching set of pads.
Examples of LDI mounting methods include chip-on-glass (COG), tape carrier package (TCP), and chip-on-film (COF). The LDI mounting methods require fine pad pitch bonding, an easy bonding process and high reliability, especially with the increasing complexity of an LDI chip arising from, for example increases in the number of pixels and high resolution. Thus, a method of forming a bump and a method of fine pad pitch bonding are key technologies.
When a conventional driving circuit is mounted on an LCD panel by using an anisotropic conductive film (ACF), the driving circuit and the LCD panel are electrically connected to each other through the conventional ACF. The AFC comprises electrically conductive particles dispersed in a non-conductive film. In the connection through the conventional ACF, the ACF is adhered to the glass TFT array substrate and the driver IC is bonded to the ACF. Thereafter, in a final bonding process, a plurality of conductive particles flows in the ACF and some of the conductive particles are captured between the bumps and the pads on the TFT array substrate, thereby electrically connecting the driving circuit to the pads and to wiring on the TFT array substrate. However, only about 10 to 30 percent of an original amount of the conductive particles are captured in the manner described, and thus much of the conductive particles are wasted. In addition, as the area of the bumps is made smaller, the number of conductive particles trapped between the bumps and the pads becomes smaller and thereby increases the resistance of the electrical connections between the bumps and the pads.
The pitch of a COG chip becomes finer as an LCD device becomes smaller, lighter and thinner, and the pitch of an outer lead bonding (OLB) or a film-on-glass (FOG) bonding also becomes finer.
When an interval between bumps of a COG chip is less than or equal to about 15 μm, an agglomeration of the conductive particles may extend from one bump to an adjacent bump, thus forming an electrical connection between the bumps to cause an electrical short defect. As noted above, as the area of the bumps decreases the number of conductive particles trapped between a pad and a bump decreases. Indeed, the number of captured conductive particles may be zero, the lack of the conductive particles causing an electrical open defect after the COG bonding.
The above-mentioned defects may be found during manufacture of an LCD or they may be found by end users of a LCD device after some time has elapsed. Thus, yield and reliability may be degraded.